Microfabrication technology has revolutionized the electronics industry. This unleashed numerous industrial applications in miniaturization and automation of manufacturing processes. The impact of microfabrication technology in biomedical research can be seen in the growing presence of microprocessor-controlled analytical instrumentation and robotics in the laboratory, which is particularly evident in laboratories engaged in high throughput genome mapping and sequencing. One area of particular-interest is the development and use of microfabricated genosensor devices for biomolecule analysis, such as a FLOW-THRU CHIP™ (“FTC”).
Microfabricated genosensor devices are compact, but with a high density of components. Known microfabricated binding devices typically are rectangular wafer-type apparatuses with a surface area of approximate one cm2 (1 cm×1 cm). The bounded regions on such devices are typically present in a density of 102-104 regions/cm2, although the desirability of constructing apparatuses with much higher densities has been regarded as an important objective. As in membrane hybridization, the detection limit for hybridization on flat-surface genosensors is limited by the quantity of DNA that can be bound to a two dimensional area. Another limitation of these approaches is the fact that a flat surface design introduces a rate-limiting step in the hybridization reaction, i.e., diffusion of target molecules over relatively long distances before encountering complementary probes on the surface. A conventional flat surface design substrate is seen in U.S. Pat. No. 5,445,934.
The FTC, which is a recent development, is a flow-through device that comprises a substrate containing first and second sides or surfaces, having a multiplicity of discrete channels extending through the-substrate from the first side to the second side. A schematic example of the FTC is shown in FIG. 1. The FTC 10 includes an ordered array of microscopic channels 13, such as channel 15 shown in greater detail, that transverse the thickness of the substrate. The FTC is particularly useful in that arrays of binding reagents, such as oligonucleotide probes, nucleic acids, and/or antibodies can be immobilized in the channels of the FTC, in spots that incorporate several microchannels. The term “probe” is used to describe a species immobilized within the microchannels and has some specific interaction with a “target” that is part of the fluid test mixture.
A major advantage of the FTCs is the uniformity of the array of microchannels and the uniformity of the individual microchannels. This characteristic distinguishes the FTCs from other three-dimensional arrays, such as porous aluminum oxide, which utilizes non-uniform hole sizes (and thus variable surface areas) and prevents straightforward normalization of results.
The FTC design allows multiple determinations to be carried out in parallel. U.S. Pat. No. 5,843,767, the entire disclosure of which is incorporated herein by reference, describes a microfabricated apparatus for conducting a multiplicity of individual and simultaneous binding reactions. The FTC design facilitates fluid flow therethrough so that biological recognition can occur within the confined volumes of the microchannels. The FTC can also be used in a variety of ways, such as a micro-reactor, concentrator, and micro-cuvette.
In practice, however, a conventional technique of holding and utilizing FTCs has led to several problems. For example, one technique of performing a hybridization assay utilizing the FTC entails placing the FTC on a small series of wells in a vacuum manifold, then placing the fluid test mixture onto the top surface thereof. Vacuum creates fluid flow. This technique, however, leads to substantial leakage problems.
Another conventional technique entails placing the FTC in a container of fluid and relying on diffusion to create the fluid flow through the microchannels. While initial capillary action draws fluid into the microchannels, blockage problems can quickly decrease the flow rate. Further, utilizing this technique is disadvantageous in that the flow rate is not selectively controllable.
Some conventional gene chip array holders (or cartridges) are commercially available. For example, a gene chip array holder is available from AFFYMETRIX. This gene chip array holder, however, operates with a non flow-through substrate. In other words, this conventional cartridge does not facilitate uniform flow during the passage of fluid through the flow-through device. Therefore, this type of conventional design is inadequate to address fluid flow and leakage issues.